FIG. 1 is an illustration of a typical conventional outboard motor assembly 100. An internal combustion engine is contained within an engine housing 104. A drive shaft (not illustrated) located within drive shaft housing 106 couples the engine to an impeller 102. As the engine operates, the drive shaft rotates, causing the propeller 102 to rotate. The rotation of the propeller 102 creates a force which causes the boat to which the outboard motor assembly 100 is attached to move.
Conventionally, certain watercraft use outboard motor assembly 100 to provide propulsion for the watercraft. The propellers of conventional outboard motor assemblies suffer from a number of disadvantages. The exposed rotating blade presents a danger to native aquatic life and to people. For example, if a person falls off the bow of a moving watercraft, the person may be dragged under the watercraft into the path of the rotating propeller 102. While there have been attempts at creating guards that encompass the propeller, such guard/propeller assemblies have typically resulted in an undesirable decrease in performance.
In addition, cavitation caused by the spinning propeller of conventional outboard motor assemblies creates inefficiencies that can result in less thrust being produced than is optimal. At certain propeller speeds, the created cavitation results in a forward speed limit, beyond which creating additional thrust is impracticable since it does not result in any meaningful improvement in the speed of the craft.
The present invention addresses the above and other problems.